A rotoreflected beam thermal lens spectrometer incorporating high-frequency modulation and the conventional double-beam concept is reported. The former enables a steady-state thermal lens to be generated, while the latter provides a means to produce a differential response that corrects for the reference absorbance automatically. The feasibility of this approach is demonstrated, and a method for improvement based on high-frequency polarization modulation is also proposed.
Yen Yang and Steven C. Hall, "Differential Thermal Lens Spectrometry Based on High-Frequency Modulation and Rotoreflective Double-Beam Configuration," Appl. Spectrosc. 42, 72-76 (1988)